ZnO-ZnFe2O4/Fe3O4/Carbon Nanocomposites for Ultrasensitive and Selective Dopamine Detection

Electrochemical detection of submicromolar levels of dopamine (DA) by iron-carbon-based redox mediators requires the capacity, and fast electron-transfer kinetics. Its absence in most reported mediators has led to detection limits that are well above the lower threshold [DA] in healthy humans (i.e., 0.01 mu M). Herein, we report a ZnO- ZnFe2O4/Fe3O4/carbon nanocomposite, which possesses the aforementioned synergy and therefore displays impressive sensing capabilities. ZnO- ZnFe2O4/Fe3O4/carbon is synthesized in situ via the carbothermal reduction of Congo red (CR)-decorated ZnO-ZnFe2O4 nanofibers. This synthesis approach allows CR-derived CO(g) to consume the lattice oxygen at the edges of ZnFe2O4 and generate oxygen vacancy (OV)-rich-Fe3O4/ ZnO interfaces embedded in mesoporous graphitic carbon. Differences in work function cause interfacial electron transfer from Fe3O4 to ZnO, which improves the Fe2+ <-> Fe3+ redox chemistry and increases the charge-carrier concentration and electron-transfer rate. Meanwhile, the lattice vacancies and surface polarization increase the surface energy, which improves DA adsorption. Benefiting from these physicochemical advantages, a nafion/ZnO-ZnFe2O4/Fe3O4/carbon-modified glassy carbon electrode (GCE) displays a low detection limit of 1.57 nM, a high sensitivity of 2.7186 AM-1 cm-2, and a rapid response time of 13 s. Crucially, it selectively detects DA in the presence of 100 times more ascorbic acid, uric acid, urea, and potassium chloride and similar levels of serotonin. In addition, it is stable, reproducible, and active in biological fluids. These properties put nafion/ZnO-ZnFe2O4/Fe3O4/carbon/GCE on the same pedestal as the current state-of-the-art and could therefore potentially be used for the practical diagnosis of DA-related diseases in biomedical applications. Therefore, our results demonstrate that the in situ carbothermic synthesis of Fe3O4 from organicdye-decorated zinc ferrite nanofiber is a useful method for improving its electrocatalytic properties. This knowledge could potentially be applied to the synthesis of an electrocatalyst for other electrochemical applications.